260 
Fishery Bulletin 95(2), 1997 
Western Gulf of Mexico 
The situation in the western Gulf of Mexico is less 
clear owing to the complexity of the physical regime 
on mesoscales of 10-100 km, coupled with the fact 
that fewer ichthyoplankton stations were made in 
this region. In this region there was no systematic 
effort to define the features that were present and to 
sample densely enough in a way that 
defined coarse scale (<10 km) distributions 
of larvae. Because surface thermal fronts 
associated with the warm-core rings are 
much more diffuse, they were difficult to 
characterize on the scale of this survey. 
Several research efforts have been directed 
to this area in an attempt to understand the 
complexities of the interaction among large 
anticyclonic rings generated by the Loop 
Current, cold dome cyclonic rings, and the 
continental shelf in the western Gulf of 
Mexico (Lewis, 1992). Only a few research 
scientists have dealt with biological compo- 
nents, but they suggest that the cyclonic cir- 
culation regions, similar to shelf waters, 
have a level of primary productivity much 
greater than that in surrounding oceanic 
waters (Biggs, 1988). Wormuth ( 1982) found 
1.5-3 times more bulk plankton volume in 
cyclonic rings than in warm-core rings. 
By comparison, the near surface waters 
of warm-core rings are oligotrophic and 
depleted in nutrients; 
therefore only near the 
ring edge were there sig- 
nificant concentrations of 
nitrate at 100 m and el- 
evated primary production 
in the upper 100 m (Biggs, 
1992). Because large anti- 
cyclonic rings are olig- 
otrophic, it is unlikely that 
mobile oceanic predators, 
such as C. pauciradiatus or 
scombrids, would be found 
within its interior where 
prey is presumably scarce. 
Despite the paucity of 
ichthyoplankton stations 
west of 89° in the Gulf, 
trends are evident. Fore- 
most of these is that larval 
C. pauciradiatus appear 
more frequently in collec- 
tions along the edges of 
both anticyclonic and cy- 
clonic rings than in tows 
made inside warm eddies 
or over the adjacent conti- 
nental margin. This find- 
-96 
-94 
-92 
-90 
-88 
-86 
-84 
Figure 14 
Diagram of transect across the Loop Current in 1988. 
Q) 
Q. 
E 
CD 
Sea surface temperature 
Cupiceps (bongo) 
Cupiceps (neuston) 
35 
30 
25 
20 
15 
10 
5 
0 
O 
c 
"O 
Figure 1 5 
Plots of transects across the Loop Current in 1987. Figure shows SST and number of C. 
pauciradiatus in bongo nets (under 10 m 2 ) and total number of larvae in the neuston net. 
Stations were two nautical miles apart. 
